1. Field of the Invention
The subject invention relates to high performance resin systems containing bismaleimides. More particularly, the subject invention relates to toughened bismaleimide resin systems prepared by adding tougheners which are alkenylphenoxy terminated polysiloxanes. The toughened resins find use as matrix resins in fiber-reinforced prepregs and composites, and as structural adhesives.
2. Description of the Related Art
Bismaleimide resin systems are noted for their high strength, high temperature performance, particularly as matrix resins in fiber-reinforced prepregs and composites. Unfortunately, bismaleimides tend to be somewhat brittle, and thus subject to impact-induced damage. For the same reasons, structural adhesives based on bismaleimides have not achieved the wide use attributable to more flexible resins such as the epoxies.
In the past, efforts have been made to toughen bismaleimides, for example, by the addition of acrylonitrile/butadiene elastomers to the resin system. Unfortunately, the degree of toughening available by this method is less than desirable. Moreover, a loss of heat resistance is seen as the amount of elastomeric toughener increases. Finally, the amount of toughener added is limited due to the formation of multiphase systems. Modifying bismaleimide systems with long chain, flexible epoxy resins has not proven successful for somewhat the same reason. Only minor amounts of epoxy resins are generally compatible with bismaleimide formulations.
The addition of alkenylphenols such as 2-allylphenol and 2-propenylphenol and their multiring homologues such as 2,2'-diallylbisphenol A has increased the toughness of bismaleimide resin systems, but once again, the degree of toughness obtained is less than that ultimately desirable. It would be desirable to prepare a toughener for bismaleimide resin systems which is compatible with other resin components, which forms a homogenous resin system and which does not cause a loss of heat resistance.